1. Field of the Invention:
The invention relates to functionalized olefinic polymers and a method of functionalizing thermoplastically processible olefinic polymers which themselves bear no functional groups.
2. Description of the Background:
A general disadvantage of all olefinic polymers is their general incompatibility with polycondensates containing a high proportion of polar groups, e.g. polyesters, polyamides, and polycarbonates. This situation is of particular concern because polyolefins, rubbers, etc. can substantially improve the impact resistance (under the notched bar test) of the polycondensates if there is good compatibility.
There are essentially two approaches by which the compatibility of polyolefins, rubbers, etc. with the polycondensates can be improved:
(1) The copolymer to be optimized is specially synthesized for the given application purpose, wherewith it contains comonomers which are chosen to improve the compatibility. This approach is very costly, because it necessitates manufacture of special products in small production amounts.
(2) One starts with readily available olefinic polymers, and functionalizes these by reacting them with monomeric alpha-beta-unsaturated carboxylic acids, anhydrides, or esters. This approach is fundamentally more advantageous. The reaction is sometimes referred to as "grafting". It may be carried out in solution or in the melt. In a number of cases it is desirable to add radical forming compounds such as azodiisobutyronitrile, di-tert-butyl peroxide, cumyl hydroperoxide, or dicumyl peroxide.
Thus, U.S. Pat. No. 3,236,917 and 3,862,265 describe grafting of unsaturated acid anhydrides to polyolefins in a roll mill and/or in the presence of a radical initiator, whereby the polyolefin becomes crosslinked. U.S. Pat. No. 3,873,643 discloses a polymeric material comprised of polyolefins with (poly)cyclic acid or anhydride groups grafted onto it, which material is manufactured in an extruder or a roll mill.
The subject of U.S. Pat. No. 3,882,194 is a method wherein a mixture of an unsaturated carboxylic acid ester and an unsaturated carboxylic acid (or anhydride of the same) is employed for grafting, preferably with the aid of peroxides.
The method described in U.S. Pat. No. 4,026,967 is distinguished in that at temperatures between 350.degree. and 500.degree. C. it brings about a rapid uncatalyzed reaction between a polyolefin and an unsaturated compound, e.g. fumaric acid. The substantial increase in melt index can be considered an indication that the polyolefins have been at least partially degraded.
Ger. OS No. 22 16 718 describes the addition of liquid unsaturated monomers such as, e.g., maleic acid anhydride, styrene, and acrylic acid, to a polyolefin melt in an extruder at elevated temperatures. As a rule, a peroxide is added at the same time. The method is feasible only if means are provided to nearly quantitatively remove the unreacted monomers.
Ger. OS No. 24 01 149 describes partial reaction of an EPDM rubber with maleic anhydride at temperatures up to 350.degree. C.
The previously known methods of functionalizing olefinic polymers all have drawbacks, i.e.,
(a) The reaction requires, as a rule, drastic reaction conditions. Typically the reaction is carried out in the melt at 200.degree.-500.degree. C. As a result, the toxic alpha-beta-unsaturated compounds are partially vaporized and pose a hazard to the operating personnel.
(b) In many cases, the reaction can be carried out in solution; however, it is unavoidably necessary to add radical formers. The molecular weight undergoes changes in the presence of free radicals, as a result of crosslinking or degradation reactions (see Ger. Pat. No. 2,216,718).
(c) A large number of commonly used acids and anhydrides are very corrosive. Therefore if they are used it is necessary to employ special protective measures.
(d) The esters are in general too volatile, and, because of the limited reactivity of the ester group, the esters are often incompatible with polycondensates.
(e) Even when radical initiators are added, the reaction seldom proceeds quantitatively.
A need continues to exist, therefore, for a better method of functionalizing olefinic polymers.